CG Board Class 8 Science Chapter 2 Solutions: Synthetic Fibres and Plastics (संश्लेषित रेशे और प्लास्टिक) – 2026-27

What are synthetic fibres?

Fibres that are synthesized or manufactured by human beings using chemical substances and chemical processes are called synthetic fibres or man-made fibres. Unlike natural fibres (such as cotton or wool), synthetic fibres are polymers made of repeating chemical units joined together. Examples include Rayon, Nylon, Polyester, and Acrylic.

Why should not we wear synthetic fabric while working in the kitchen?

Synthetic fibres melt on heating, which is a major disadvantage. If synthetic clothes catch fire accidentally, the fabric melts and shrinks, sticking tightly to the body of the person wearing it and causing severe, painful burns. Therefore, one should never wear synthetic clothes while working in the kitchen near an open flame or in a chemical laboratory.

Polymers are made up of smaller units called monomers. Explain with an example.

A polymer is a very large single unit formed by joining together hundreds or thousands of small repeating chemical units called monomers (where mono = single, mer = unit; poly = many).

Examples:

1. Natural Polymer Example: Cellulose (found in cotton) is a natural polymer made up of a large number of glucose monomer units joined in a long chain.
2. Synthetic Polymer Example: Polythene is a synthetic plastic polymer formed by joining many ethene monomer molecules together.

Chemical Reaction Equation:

n (Ethene Monomers) → [Polymerization] -[CH₂-CH₂-]_n (Polythene Polymer)

Differentiate between thermoplastic and thermosetting plastics.

Why electrical switches are made from thermosetting plastics?

Electrical switches are made specifically from thermosetting plastics (such as Bakelite) because:

1. Electrical Insulation: Bakelite is a poor conductor of electricity, preventing electric shocks and ensuring safe handling.
2. Thermal Resistance: Thermosetting plastics do not melt or deform even when high heat is generated inside the electrical circuit during prolonged current flow.

Plastics are a cause of environmental pollution. Explain by giving two examples.

Plastics are non-biodegradable materials that take hundreds of years to decompose naturally, making them a major source of environmental pollution.

Two Examples:

1. Clogging of Drainage Systems: Discarded plastic bags and bottles get washed into sewage drains, blocking the flow of water and causing unsanitary waterlogging in urban areas.
2. Hazard to Soil and Animals: Stray animals like cows ingest discarded plastic bags while eating food waste, which clogs their digestive system and leads to fatal consequences. Additionally, plastics buried in soil prevent rainwater percolation, harming root growth and soil fertility.

Synthetic fibres are:

(a) Fibres obtained from plants

(b) Fibres obtained from animals

(c) Fibres made from chemicals

(d) All the above

(c) Fibres made from chemicals / (c) रसायनों से निर्मित रेशे

The type of plastic used in making combs is:

(a) Thermosetting plastic

(b) Thermoplastic

(c) (a) and (b) both

(d) Neither (a) nor (b)

(b) Thermoplastic / (b) थर्मोप्लास्टिक

Clothes of firemen are made from:

(a) Teflon

(b) Melamine

(c) Bakelite

(d) Thermoplastic

(b) Melamine / (b) मेलामाइन से

Artificial silk is:

(a) Nylon

(b) Polyester

(c) Rayon

(d) Acrylic

(c) Rayon / (c) रेयॉन

PET is:

(a) Nylon

(b) Polyester

(c) Rayon

(d) Acrylic

(b) Polyester / (b) पॉलिएस्टर

Answer Table:

Name any three objects made from nylon that shows its strength.

Nylon thread is exceptionally strong, elastic, and light; a single nylon thread is actually stronger than a steel wire of comparable thickness. Three objects made from nylon that demonstrate its high mechanical strength are:

Why PET containers are preferred to store food items?

PET (Polyethylene Terephthalate) is a widely used form of polyester. PET bottles and containers are preferred over traditional glass or metal containers for storing food items, water, and pickles due to the following reasons:

1. Chemical Non-reactivity: PET is non-reactive and does not react with water, food constituents, or mild organic acids present in pickles, ensuring food safety.
2. Lightweight and Shatterproof: PET containers are light in weight, highly durable, and unbreakable compared to fragile glass jars.
3. Moisture-proof and Clear: They provide a strong barrier against external moisture, keeping stored food crisp and clean while offering transparent visibility.

Manufacturing of synthetic fibres has a beneficial role in conservation of forests. Explain.

Natural fibres like cotton, linen, and jute are derived from plants, requiring extensive deforestation and agricultural land clearings. Furthermore, obtaining Rayon (artificial silk) requires large quantities of wood pulp, which is obtained by cutting down millions of forest trees.

On the other hand, fully synthetic fibres like Nylon, Polyester, and Acrylic are synthesized chemically using petrochemicals without utilizing raw materials derived from plants or trees. By substituting natural timber-derived materials and natural plant fibres with synthetic fibres, the demand for cutting down forest trees is significantly reduced. Therefore, the manufacturing and widespread adoption of synthetic fibres play a vital and beneficial role in the conservation of forests.